Grade IV Practice Exam Questions And

New Hampshire Wastewater Operator Grade IV Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• The primary purpose of preliminary treatment in a wastewater plant is

to:

• Remove dissolved organics
• Remove pathogens
• Remove large solids and grit
• Remove nutrients

Rationale: Preliminary treatment is designed to remove large debris,

sand, and grit to protect downstream equipment.

2. The design of a trickling filter primarily depends on:

• Flow rate and temperature 1 / 4

• Organic loading and hydraulic loading
• pH and alkalinity
• Dissolved oxygen concentration

Rationale: Trickling filter design is based on both the organic load to

be treated and the hydraulic flow rate to ensure proper contact time and treatment.

3. The main goal of secondary treatment is to:

• Remove grit
• Reduce BOD and suspended solids
• Disinfect the effluent
• Remove nitrogen

Rationale: Secondary treatment focuses on biological processes that

reduce biochemical oxygen demand (BOD) and suspended solids.

• What is the typical sludge volume index (SVI) range for good settling

activated sludge?

• 20–50 mL/g
• 100–150 mL/g
• 200–250 mL/g
• 300–350 mL/g

Rationale: An SVI of 100–150 mL/g indicates well-settling sludge in

conventional activated sludge systems.

5. A sudden increase in influent BOD can cause:

• Increased sludge age 2 / 4

• Reduced aeration requirements
• Oxygen depletion and possible effluent violation
• Improved disinfection efficiency

Rationale: High influent BOD increases oxygen demand, potentially

leading to oxygen depletion and poor treatment performance.

6. Nitrification in wastewater treatment converts:

• Nitrite to nitrogen gas
• Ammonia to nitrogen gas
• Ammonia to nitrate
• Nitrate to ammonia

Rationale: Nitrification is the biological oxidation of ammonia to

nitrate, usually in two steps: ammonia to nitrite, then nitrite to

nitrate.

7. Denitrification requires:

• Aerobic conditions
• Anoxic conditions with a carbon source
• High pH and high temperature
• UV light

Rationale: Denitrification is an anoxic process where nitrate is

reduced to nitrogen gas using a carbon source.

8. In a sequencing batch reactor (SBR), the reaction phase is:

• Only filling
• Aeration and mixing 3 / 4

• Decanting
• Settling

Rationale: During the reaction phase, the SBR aerates and mixes

wastewater to promote biological treatment.

• Which disinfectant is most commonly used in U.S. wastewater plants?
• Ozone
• UV
• Chlorine
• Hydrogen peroxide

Rationale: Chlorine is the most widely used disinfectant due to cost-

effectiveness and reliability.

10. The primary concern with chlorine gas storage is:

• Toxicity and corrosion
• Flammability
• Explosiveness
• Radioactivity

Rationale: Chlorine is highly toxic and corrosive, requiring careful

handling and storage.

11. BOD5 represents:

• Total organic carbon in five minutes
• Biochemical oxygen demand over five days
• Oxygen demand in 5 hours
• Chemical oxygen demand over five days
• / 4